Thursday 20 February 2014

Why I think the 2nd wave of human influenza A(H7N9) virus infections has broken...

If you look at the chart above, it shows declining:

  • Average cases per day (blue data points) in 2014
  • Less noticeable but consistently declining average cases per day when calculated across all of Wave 2 (oranges data points)
  • And importantly, a drastic decline in the number of new cases being announced after the 27-Jan peak. 

From 5-Feb, we have not seen more than 2 cases/day whereas in Jan we were regularly seeing 5-6 cases/day (peaking at 12/day).

The last time we saw this steep a drop in cases was 19-Apr 2014; the end of H7N9's 1st wave of human infections. 

That doesn't mean the virus has gone away or that the outbreak has been "solved". I learned that lesson last year. H7N9 is still out there. 

If these latest case numbers accurately reflect what is happening in China, then it looks like closing poultry markets did the same job in 2014 that it did in halting the 2013 Spring outbreak in southeast China. It will be down to the poultry industry and perhaps the Ministry of Agriculture in China to find evidence that specifically disproves a role for poultry in human infections; and it seem clear that changing from fresh to processed poultry has some even more safety data to support it.

We still have no data that lets us point the finger at chickens, or ducks or song birds or pigeons or geese or some other animal in the markets as the source. 

We just know there is a strong association between humans getting infected after being in the presence of "live poultry" usually in a market setting. With reports suggesting better growth of H7N9 in song birds compared to chickens as well as poor spread of virus between infected chickens, there is much work to be done outside of chickens to track the source of the virus down.

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